1. Field of the Invention
The present invention relates to a power amplifier, and more particularly, to a predistortion linearizer that is capable of improving a nonlinear characteristic, and its method.
2. Description of the Background Art
Generally, a power amplifier is used to increase power of a radio frequency (RF). An ideal power amplifier would increase only the magnitude without distorting an input RF signal.
However, since the power amplifier typically includes an active device having a nonlinear characteristic, an output of the power amplifier inevitably includes a distortion component. Thus, in order to improve the nonlinear characteristic of the power amplifier, various linearization techniques and algorithms are proposed. Typical linearization methods include a predistortion method, an envelope feedback method and a feedforward method or the like.
FIG. 1 shows the construction of a linearizer of a power amplifier adopting the feedforward method in a base station transmitting apparatus in accordance with a conventional art.
As shown in FIG. 1, a linearizer of a conventional power amplifier includes a main path unit 100 and a distortion signal detecting unit 200.
The main path unit 100 includes a modem 110 for generating a source signal; an analog baseband unit 120 for converting the generated source signal to a baseband analog signal; an up converter 130 for up-converting the converted analog signal; a gain and phase controller 140 for controlling a gain and a phase of the up-converted signal; a high power amplifier (HPA) 150 for amplifying the output signal of the gain and phase controller 140; a delay unit 160 for delaying the output signal of the HPA 150; a combiner 170 for combining the output signal of the delay unit 160 and the distortion signal generated from the distortion signal detecting unit 200 and removing a distortion component contained in the output signal of the HPA 150; a filter 180 for filtering the output signal of the combiner 170; and a transmission unit 190 for transmitting the filtered signal.
The distortion signal detecting unit 200 includes a delay unit 210 for delaying the output signal of the up-converter 130; a combiner 220 for combining the output signals of the delay unit 210 and the HPA 150 and detecting a distortion component contained in the output signal of the HPA 150; a gain and phase controller 230 for controlling a gain and a phase of the distortion signal detected by the combiner 220; and a distortion amplifier 240 for amplifying the output signal of the gain and phase controller 230 and outputting it to the combiner 170 of the main path unit 100.
The operation of the linearizer of the power amplifier adopting the feedforward method of the conventional art will now be described with reference to FIG. 1.
The source signal generated by the modem 110 is converted into a baseband analog signal by the analog baseband unit 120 and then converted into a radio frequency signal 130a. The converted radio frequency signal 130a is gain and phase-controlled by the gain and phase controller 140 and amplified to a predetermined level by the HPA 150.
At this time, the combiner 220 of the distortion signal detector 200 combines the output signals 130a and 150a of the up-converter 130 and the HPA150 which have been delayed by the delay unit 210, detects a distortion signal 220a contained in the output signal 150a of the HPA 150, and inputs the detected distortion signal 220a through the gain and phase controller 230 and the distortion amplifier 240 to the combiner 170 of the main path unit 100.
The combiner 170 combines the output signal 150a of the HPA 240 which has been delayed by the delay unit 150 and the distortion signal 220a amplified by the distortion amplifier 240, and outputs only an input signal 130b without the distortion component.
A spurious component of the output signal 130b of the combiner 170 is removed by the filter 180 and then the output signal without the spurious component is transmitted through the transmission unit 190.
However, as for the linearizer of the conventional power amplifier, if the input signal provided as an input of the power amplifier is distorted, an output signal of the power amplifier inevitably contains a distortion component no matter how excellent the performance of the power amplifier is.
Thus, in the linearizer of the conventional power amplifier, when the up-converter performs a frequency up converting, an output signal of the up-converter may contain the distortion component, which becomes an obstacle to improvement of the nonlinear characteristic of the power amplifier.
In order to improve the nonlinear characteristic of the conventional power amplifier, the final output of the power amplifier is lowly backed off so that the power amplifier can be linearly operated for the whole change interval of an input signal. In such a case, however, an efficiency of the power amplifier is much degraded.
In addition, the linearizer adopting the feedforward method exhibits a low efficiency compared to other linearization methods.